1. Field of the Invention
The present invention generally relates to a three-electrode-discharge surge arrester and, more particularly, to a three-electrode-discharge surge arrester eliminating a surge current generated between two line wires and a ground wire.
2. Description of the Related Art
A description will now be given, with reference to FIG. 1, of a conventional three-electrode-discharge surge arrester.
The conventional three-electrode-discharge surge arrester has a pair of axially placed line electrodes 10 formed of metals such as Fexe2x80x94Ni alloys, with a predetermined gap therebetween, so that cylindrically shaped discharging parts 12 provided respectively on the inner edges of the pair of line electrodes 10 oppose each other.
Between the opposing discharging parts 12 of the pair of line electrodes 10 is a ground electrode 20 provided with a penetration hole 28 in the center.
Between the ground electrode 20 and each of the line electrodes 10 is each of a pair of cylindrical insulating housings 30, within each of which the discharging part 12 of the line electrode 10 is inserted. The cylindrical insulating housings 30 are formed of insulators such as ceramic. Circular electric terminals 14 formed respectively on the outer side of the pair of line electrodes 10 seal the outer openings of the pair of cylindrical insulating housings 30 airtight. The cylindrical insulating housings 30 are placed airtight between each of the line electrodes 10 and the ground electrode 20.
A terminal 24 of the ground electrode 20 is held between the pair of cylindrical insulating housings 30. The circumference of the terminal 24 of the ground electrode 20 exposes itself between the pair of cylindrical insulating housings 30.
In the conventional three-electrode-discharge surge arrester shown in FIG. 1, two line wires (not shown in the figure) can be connected to the circular electric terminals 14 sealing the outer openings of the pair of cylindrical insulating housings 30, respectively. Also, a ground wire (not shown in the figure) can be connected to the terminal 24 of the ground electrode 20 exposing itself between the pair of cylindrical insulating housings 30. Then, a surge current generated between either of the two line wires and the ground wire can be eliminated by causing a discharge to occur in a gap between either of the discharging parts 12 of the line electrodes 10 and its opposing discharging part 22 of the ground electrode 20.
However, in the above-mentioned conventional three-electrode-discharge surge arrester, when a discharge occurs between each of the discharging parts 12 of the line electrodes 10 and its opposing discharging part 22 of the ground electrode 20, particles of metals such as Fexe2x80x94Ni alloys forming the discharging parts 12 and 22 disperse from the discharging parts 12 and 22 by sputtering, to land on the inner peripheral surfaces of the cylindrical insulating housings 30. Then, the sputtered particles, unduly connected with conductive trigger lines 32, which are formed on the inner peripheral surfaces of the cylindrical insulating housings 30 and electrically connected to the line electrodes 10 and the ground electrode 20, cause deteriorated insulation between each of the line electrodes 10 and the ground electrode 20. This prevents stable and accurate discharges from occurring repeatedly over a long period of time between each of the discharging parts 12 of the line electrodes 10 and its opposing discharging part 22 of the ground electrode 20.
It is a general object of the present invention to provide an improved and useful three-electrode-discharge surge arrester in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a three-electrode-discharge surge arrester which can cause stable and accurate discharges to occur repeatedly over a long period of time and can eliminate a surge current generated between two line wires and a ground wire.
In order to achieve the above-mentioned objects, there is provided according to the present invention a three-electrode-discharge surge arrester having two discharging parts of a pair of line electrodes, the two discharging parts opposing each other and defining a gap therebetween; a ground electrode disposed between the two discharging parts and provided with a penetration hole in the center thereof; and two cylindrical insulating housings between each of the line electrodes and the ground electrode,
wherein each of the two discharging parts has a substantially conical shape; each of inner surfaces of upper and lower parts of the penetration hole is substantially funnel-shaped, in accordance with the substantially conical shape; and oblique parallel gaps for a primary discharge are formed between the inner surfaces of the upper and lower parts of the penetration hole and the two discharging parts, respectively,
wherein parallel gaps for a secondary discharge are formed between peripheral parts of the ground electrode around the penetration hole and peripheral parts of the pair of line electrodes, respectively, each of the peripheral parts of the pair of line electrodes opposing each of the peripheral parts of the ground electrode around the penetration hole, and
wherein each of the oblique parallel gaps is formed narrower than each of the parallel gaps.
The three-electrode-discharge surge arrester according to the present invention has the substantially conical discharging parts of the line electrodes. To suit this shape, the upper and lower parts of the penetration hole of the ground electrode each have the substantially funnel-shaped inner surfaces. Between each of the substantially conical discharging parts of the line electrodes and its opposing substantially funnel-shaped inner surface of the penetration hole of the ground electrode is the oblique parallel gap for a primary discharge.
Therefore, when a primary discharge occurs in the oblique parallel gaps formed between each of the substantially conical discharging parts of the line electrodes and each of the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, metal particles are sputtered from the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode. However, the sputtering is blocked by the ground electrode around the penetration hole and the discharging parts of the line electrodes, so that the sputtered metal particles are kept from landing on the inner peripheral surfaces of the cylindrical insulating housings each placed between the ground electrode and each of the line electrodes. This prevents deteriorated insulation, otherwise caused by the sputtering, between each of the line electrodes and the ground electrode.
Also, the metal particles sputtered from the substantially conical discharging parts of the line electrodes land on the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, and the metal particles sputtered from the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode land on the opposing substantially conical discharging parts of the line electrodes. Therefore, the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode keep supplementing sputtered metals to each other.
This prevents changing significantly the width and length of the oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, because metals forming the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, respectively, keep supplementing each other and do not eventually disappear, when primary discharges occur repeatedly over a long period of time between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode. Therefore, stable and accurate discharges at a predetermined electric potential occur repeatedly over a long period of time in the oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode.
Additionally, when a large surge voltage is provided between the line electrode and the ground electrode, a primary discharge occurring in the oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode is followed by a secondary discharge occurring in the relatively wider parallel gaps between the peripheral parts of the ground electrode around the penetration hole and the opposing peripheral parts of the line electrodes. This secondary discharge occurring in the parallel gaps surely eliminates the above-mentioned large surge voltage.
Additionally, because the oblique parallel gaps are narrower than the parallel gaps, when a not quite as large surge voltage is provided between the line electrode and the ground electrode, a primary discharge occurs in the relatively narrower oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode. This primary discharge occurring in the oblique parallel gaps surely eliminates the above-mentioned not quite as large surge voltage.
With this not quite as large surge voltage, since a secondary discharge does not occur in the relatively wider parallel gaps between the peripheral parts of the ground electrode around the penetration hole and the opposing peripheral parts of the line electrodes, metal particles are kept from sputtering from the peripheral parts of the ground electrode and the opposing peripheral parts of the line electrodes and landing on the inner peripheral surfaces of the cylindrical insulating housings. This prevents deteriorated insulation, otherwise caused by the sputtering, between each of the line electrodes and the ground electrode.
Additionally, because the discharging parts of the line electrodes are substantially conical and, to suit this shape, the inner surfaces of the upper and lower parts of the penetration hole of the ground electrode are substantially funnel-shaped, the area of each of the oblique parallel gaps formed therebetween for a primary discharge can be increased, compared with the conventional three-electrode-discharge surge arrester having substantially cylindrically shaped discharging parts of a pair of line electrodes and, correspondingly, substantially cylindrically shaped inner surfaces of upper and lower parts of a penetration hole of a ground electrode. Therefore, stable primary discharges occur repeatedly over a long period of time in the oblique parallel gaps increased in area.
Additionally, the substantially conical discharging parts of the line electrodes can be easily and surely formed by coining, compared with the substantially cylindrically shaped discharging parts of the line electrodes. This is remarkably effective especially when substantially conical small-sized discharging parts of a diameter equal to or less than 6 mm are formed by coining.
In the three-electrode-discharge surge arrester according to the present invention, discharge activating materials are preferred to be applied to the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the upper and lower parts of the penetration hole of the ground electrode.
In the three-electrode-discharge surge arrester having this structure, the discharge activating materials applied to the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode cause a primary discharge to occur smoothly and surely in the oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode.
Additionally, when a primary discharge occurs in the oblique parallel gaps formed between each of the substantially conical discharging parts of the line electrodes and each of the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, particles of the discharge activating materials applied to the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode disperse due to sputtering. However, the sputtered particles are blocked by the ground electrode around the penetration hole and the discharging parts of the line electrodes, so that the sputtered particles are kept from landing on the inner peripheral surfaces of the cylindrical insulating housings each placed between the ground electrode and each of the line electrodes. This prevents deteriorated insulation between each of the line electrodes and the ground electrode, otherwise caused by the sputtering.
Also, when a primary discharge occurs, sputtered particles of the discharge activating materials applied to the surfaces of the substantially conical discharging parts of the line electrodes land on the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode, and sputtered particles of the discharge activating materials applied to the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode land on the opposing substantially conical discharging parts of the line electrodes. Therefore, the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode keep supplementing the sputtered discharge activating materials to each other.
This prevents the discharge activating materials applied to the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode from dispersing away due to sputtering and eventually disappearing, when primary discharges occur repeatedly over a long period of time between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode. Therefore, the discharge activating materials remaining on the surfaces of the substantially conical discharging parts of the line electrodes and the substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode cause primary discharges to occur repeatedly and stably over a long period of time in the oblique parallel gaps between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode.
Additionally, when highly fluid discharge activating materials are applied to the surfaces of the substantially conical discharging parts of the line electrodes, the substantially conical shape thereof prevents the discharge activating materials from running down, pulled by gravity force, the surfaces of the substantially conical discharging parts of the line electrodes, and allows the discharge activating materials to be applied surely and substantially evenly to the surfaces of the substantially conical discharging parts of the line electrodes, compared with the conventional three-electrode-discharge surge arrester having the substantially cylindrically shaped discharging parts of the line electrodes.
Additionally, the three-electrode-discharge surge arrester according to the present invention is preferred to have annular concave portions on the boundaries between the substantially conical discharging parts and the adjacent peripheral parts on the line electrodes, respectively. The annular concave portions are used for collecting an excess amount of the discharge activating materials applied to the surfaces of the substantially conical discharging parts of the line electrodes.
In the three-electrode-discharge surge arrester having this structure, when liquefied discharge activating materials are applied to the surfaces of the substantially conical discharging parts of the line electrodes, an excess amount of the discharge activating materials, running down from the surfaces of the substantially conical discharging parts of the line electrodes toward the surfaces of the adjacent peripheral parts of the line electrodes, flows into the annular concave portions and is collected therein. Therefore, the three-electrode-discharge surge arrester having this structure prevents the discharge activating materials from being applied widely, affected by surface tension, around the surfaces of the peripheral parts of the line electrodes adjacent to the surfaces of the substantially conical discharging parts of the line electrodes. Hence, the three-electrode-discharge surge arrester having this structure prevents a primary discharge from occurring between the peripheral parts of the line electrodes and the opposing peripheral parts of the ground electrode, respectively, affected by the discharge activating materials applied around the surfaces of the peripheral parts of the line electrodes. Accordingly, the three-electrode-discharge surge arrester having this structure prevents a primary discharge from occurring unsurely in the oblique parallel gaps formed between the substantially conical discharging parts of the line electrodes and the opposing substantially funnel-shaped inner surfaces of the penetration hole of the ground electrode.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.